The present invention relates to a coating composition containing polyvinyl butyral, in particular a coating composition which has especially superior properties such as scratch resistance and chemical resistance and additionally is capable of forming a transparent film rich in flame retarding property.
Polyvinyl butyral (which will be referred to as butyral resin hereinafter), prepared by the steps of saponifying polyvinyl acetate with alkali to obtain polyvinyl alcohol and then subjecting the resulting polyvinyl alcohol to acetalation with butyraldehyde or by performing said saponification and acetalation at the same time, has hitherto been utilized in adhesives, paints and the like and has been widely used in intermediate films for safety glasses as well. However, in view of the fact that said butyral resin, when utilized as coating agent for the purpose of protecting the surface of a substrate, has proved to be defective in that the resulting film is insufficient not only in scratch resistance but also in chemical resistance and inflammability, the application of butyral resin to coating agents has been extremely limited.
The present invention intends to provide a novel coating composition which has successfully eliminated the aforesaid drawbacks, pointed out as being inherent in butyral resin, by the use of colloidal silica. The coating composition according to the present invention is capable of forming on the surface of a substrate a transparent film possessing characteristics such as scratch resistance, chemical resistance an flame retarding property, and therefore it can broaden the utilization of butyral resin as a coating agent.